Back in November, Google sent a letter to the FCC which that was recently made available to the public. The letter explained that Google would add support for Band 48 for the Pixel 3 with the model number G013A. This number includes all Pixel 3 devices sold internationally and via Verizon but excludes the Japanese variant.
Band 48 in the United States is currently used for the Citizen Broadband Radio Service (CBRS) or CB Radio. The software update would allow the Pixel 3 to connect to a carrier tower that is running on the unlicensed LTE band.